I was wondering how the word "you" is being used in the phrase "you dirty rat" (think James Cagney). Other similar phrases are Judy Garland's "You Wonderful You" or insults such as "What the noun, you adjective noun!" I imagine that phrases like this started out with digs at one's siblings, "You, the stink-head over there, pass me the muffin," but this took too long, and so we got, "Pass me the muffin, you stink-head."
Am I right about this? Is it ever OK to use these phrases in writing? If so, should there be commas like, "you, dirty rat?"
One more question:
Take the sentence, "You dirty rat, you stole my knish!" Then "You" and "rat" in the phrase "You dirty rat" are both appositives with "rat" in apposition to "You" and "You" in apposition to the subject of the sentence. Is this right?
This all gets very ugly, by the way, when trying to diagram the sentence, "You break my heart, you, you wonderful you."